The broad objective of these investigations is to define the mechanisms by which various hormones and non-humoral agents regulate the metabolism and differentiation of bone cells, and determine their roles in modifying the structure and function of bone. We will utilize isolated, viable cells dispersed from well differentiated bone, thereby circumventing difficulties encountered in studying intact bones and bone segments in vitro. Bone cells isolated by methods developed in this laboratory have already been shown to perform certain differentiated functions, and to respond to physiological concentrations of bone seeking hormones, including adrenal glucocorticoids and parathyroid hormone. We will extend ongoing studies in 3 major areas: the regulation of bone cell adenylate cyclase activity by adenosine and related compounds, the regulation of bone cell cyclic 3'5' AMP metabolism by parathyroid hormone and calcitonin, and the separation and culture of morphologically and functionally distinct classes of bone cells. Embodied in these studies will be experiments designed to demonstrate the presence of a specific adenosine receptor on the bone cell surface, explore the mechanism whereby bone cells become refractory to parathyroid hormone after an initial period of treatment, examine the possibility that parathyroid hormone and calcitonin affect the metabolism of separate types of bone cells, and develop a method for culturing bone cells in a chemically defined medium.